Last but not least

Meaning

An introduction, often on stage, indicating that the person announced last is no less important than those introduced earlier.

Origin

We know 'last but not least' best from its use in the theatre. In Variety theatre especially it was a commonplace part of introductions and that usage was presumably encouraged by the fact that the star turn invariably came on last. The origin of last but not least is uncertain - the first reference to it that I can find in print is from John Lyly's Euphues and His England, 1580.

I have heard oftentimes that in love there are three things
for to be used: if time serve, violence, if wealth be great, gold, if
necessity compel, sorcery. But of these three but one can stand
me in stead - the last, but not the least'; which is able to work
the minds of all women like wax

The idea, if not the actual phrase, may have been inspired the Bible, where a similar thought is expressed - in Matthew 19:30 (John Wyclif's version ), 1382, we find:

But manye schulen be, the firste the laste, and the laste the firste.

Shakespeare later used a version of the phrase in King Lear, 1605:

KING LEAR:
To thee and thine hereditary ever
Remain this ample third of our fair kingdom;
No less in space, validity, and pleasure,
Than that conferr'd on Goneril. Now, our joy,
Although the last, not least; to whose young love
The vines of France and milk of Burgundy
Strive to be interess'd; what can you say to draw
A third more opulent than your sisters? Speak.